kern/118093: firewire bus reset hogs CPU, causing data to be lost

[Sean Bruno]

The following reply was made to PR kern/118093; it has been noted by GNATS.

From: Sean Bruno <sbruno at miralink.com>
To: "M. Warner Losh" <imp at bsdimp.com>
Cc: freebsd at sopwith.solgatos.com, freebsd-firewire at freebsd.org, 
 bug-followup at freebsd.org
Subject: Re: kern/118093: firewire bus reset hogs CPU, causing data to be
 lost
Date: Wed, 17 Dec 2008 17:10:53 -0800

 M. Warner Losh wrote:
 > In message: <200812170329.DAA17848 at sopwith.solgatos.com>
 >             Dieter <freebsd at sopwith.solgatos.com> writes:
 > : Sean>  Which file in dev/firewire are you looking at?
 > : 
 > : fwohci.c  and  firewire.c
 > : 
 > : examples:
 > : 
 > : printf("non CYCLEMASTER mode\n");
 > : 
 > : device_printf(fc->dev, "Initiate bus reset\n");
 > : 
 > : -------------------
 > : 
 > : Warner>  This can't be the case.  There's no SPL involved at all.  Maybe
 > : Warner>  removing the printfs causes an interrupt to be serviced faster,
 > : Warner>  resulting in what appears to be better performance...
 > : 
 > : With the printfs, Ethernet is not getting serviced.  This
 > : is repeatable and easily reproduced.   Without the printfs,
 > : it seems ok.
 > : 
 > : If it isn't spl, what is locking out Ethernet?
 >
 > interrupt storm?  In old-spl-locked drivers, often times the interrupt
 > would be masked while certain operations happened.  In new
 > mutex-locked freebsd, there's no way to block the interrupts, so
 > sometimes old code gets into an interrupt storm, which starves other
 > things.  Not sure why printf would trigger this, however...
 >
 > Warner
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 >   
 Let me take a stab at this one this week.  There's got to be something 
 more going on
 than a printf() causing hell.  It could be a mutex being held causing 
 nightmares.
 
 The firewire code is my current project, I'll look at this issue now.
 
 Sean